As a distortion correction technology that has been widely used in recent years, a digital pre-distortion scheme is known.
The digital pre-distortion scheme serves to correct nonlinear distortion that occurs in electric power amplifiers and that has been used in envelope detection type linear analyzers presented in Patent Literature 1.
Concretely, in the digital pre-distortion scheme, a transmission signal inputted to a power amplifier and a feedback signal of a signal outputted from the power amplifier are compared with respect to their amplitudes and phases and then a distortion correction coefficient that represents the invert characteristic of a nonlinear characteristic of the electric power amplifier is obtained based on the comparison result, and then a complex-multiplication is performed for the transmission signal and the obtained distortion correction coefficient. The resultant complex-multiplied signal is inputted to the power amplifier and thereby the nonlinear distortion is corrected.
To perform the comparison process for the transmission signal and the feedback signal, their timings need to match. To match the timings of the transmission signal and the feedback signal, a method as presented in Patent Literature 2 is known in which the time lag between the transmission signal and the feedback signal is changed at each sampling period, the correlation value between the transmission signal and the feedback signal is computed, the delay time is decided based on the maximum correlation value of the obtained correlation values, and then the timings of the transmission signal and the feedback signal are matched using the decided delay time.